Helical coil-on-tube heat exchanger

ABSTRACT

A coil on tube heat exchanger is provided that uses multiple parallel helical coil tubes to limit liquid pressure losses while providing similar performance and production times to previous coil and tube designs. Two or more coil tubes are wrapped together around a tube in a helical fashion, permitting the heat exchanger to be used in a counter-flow, or contra-flow, implementation. The system preferably includes a header, or manifold, to connect two or more of the coil tubes together at the beginning and/or end of the tube. However, each individual coil may be connected to a separate load and kept independent. Embodiments of the present invention provide reduced pressure loss, higher performance and are generally faster to manufacture than prior heat exchangers.

FIELD OF THE INVENTION

The present invention relates generally to heat exchange devices. Moreparticularly, the present invention relates to coil-on-tube heatexchangers.

BACKGROUND OF THE INVENTION

Heat exchange devices, or heat exchangers, are devices for transferringheat from one medium to another, typically from one fluid to another orto the environment, without allowing the fluids to mix. Some examplesare: automobile radiators; air conditioners, which use both a condenserand an evaporator; and steam and hot water radiators, which are used toproduce heat. In order to prevent mixing of the fluids, or liquids, abarrier is provided between the two liquids or media. Many differentheat exchanger barrier designs are used. In a “plate and frame” design,which is very compact, two liquid streams pass on opposing sides of oneor more plates. The total heat transfer surface may be increased byincreasing the area of plates and the number of plates. In a “tube andshell” design, one stream of liquid flow passes through the tube(s) andthe other through the remaining space inside a shell that surrounds thetubes. A special subcategory the tube and shell design would be animmersion coil type design, such as a heating coil in a tank. However,both the “plate and frame” and “tube and shell” designs are susceptibleto fouling and clogging. These drawbacks are considerable whenconsidering applications relating to treatment of waste water.

A particular application of heat exchangers is in the area of wastewater heat reclamation or “recovery”. There are many examples of both“tube and shell” and “plate and frame” waste water systems. However,many of these systems often require a filter, because they aresusceptible to clogging and/or fouling due to the nature of theirdesign. Also, in addition to the heat exchanger itself, it is oftennecessary to have an elaborate apparatus to perform the actual wastewater treatment. Some of these systems include coils, but these coilsare often a part of a tube and shell design, such as an immersion coil.

Helical coil-on-tube heat exchangers have been in use for some time.This type of heat exchanger typically consists of a single coil that iswrapped around a tube. Prior coil-on-tube heat exchangers have been usedas direct-fired water heaters, in which combustion takes place withinthe tube, warming the liquid in the coil. Coil-on-tube heat exchangersare also used for waste-water heat recovery.

Typical liquid flow rates have traditionally been modest using thesingle coil design. More recent applications of this class of heatexchanger, such as wastewater heat recovery, have resulted in muchhigher liquid flow rates. Coil-on-tube type heat exchangers have asignificant advantage in wastewater applications as the center tubeallows the waste water to pass through easily without clogging.Production rates for single-coil-on-tube heat exchangers are low andprovide good performance.

However, in many applications, desired flow rates result in a largepressure loss in single-coil designs. The loss is generally proportionalto the distance travelled in the coil, the second order of the flowrate, and is inversely proportional to the cross-sectional area. Whenlong lengths of coil are required, the resulting pressure loss is notacceptable for many applications.

By increasing the number of liquid pathways on the coil side of the heatexchanger, pressure loss can be reduced. Coil-on-tube heat exchangershaving multiple coils exist, with different designs being typically usedfor different applications. The number of coils used depends on themaximum desired flow rate. The higher the desired flow rate, the morecoils are needed to keep pressure losses to a reasonable amount. Forexample, in a single residential installation, such as most houses, a ½inch nominal tube is used for a coil, and 1 to 2 coils are used. Forapartment buildings, 2 to 4 coils are typically used, and in commercialsettings (such as health clubs, etc.), several coils are typically usedby manifolding heat exchangers. Each design is not necessarily limitedto a given application (a 4 coil unit could be used for a commercial ora residential application). The important thing is that the number ofcoils be high enough to keep the pressure loss low enough for the flowrate in a given application.

FIG. 1 illustrates a conventional heat exchanger with multiple coils,each provided as single-coil helixes. In such a known design of a heatexchanger 10, a center tube 12 is provided having a center tube inletend 14 and a center tube outlet end 16. In the two-coil heat exchanger10 of FIG. 1, a first coil 18 is located around a first portion of thetube 12 and a second coil 20 is located around a second portion of thetube 12. The first coil 18 has a first coil inlet end 22 provided nearthe center tube outlet end 16 and a first coil outlet end 24 providednear the mid-point of the length of the center tube 12. The second coil20 has an inlet end 26 provided near the mid-pointof the length of thecenter tube 12 and an outlet end 28 provided near the center tube inletend 14. The use of the terms inlet and outlet ends above presumes that aliquid flow in the center tube 12 is in a different direction that theliquid flow in the first and second coils 18 and 20.

The total liquid inflow for the coils is thus divided into two so that aportion of the incoming liquid flows to each of the two coils 18 and 20,entering at an the inlet end thereof. This reduces the overall liquidpressure loss through the coils as compared to the single coil design.However, to accomplish this, a header or manifold is required to connectthe multiple coils together, since the inflow points and outflow pointsof the heat exchanger are spread out over the length of the center tube.The different coils will not perform their function without the header,since without the header the inflow could only reach the first coil, andthe outflow of the first coil could not output at the outflow and of thecenter tube. The header can include an inflow header 30 and the outflowheader 32, connecting the inflow and outflow ends of the coils,respectively.

Although the coils are able to treat flows or liquid in parallel witheach other, the coils are themselves placed on succeeding distinctlongitudinal sections of the center tube. As mentioned above, thetreatment of parallel flows of liquid requires that the heat exchangerinclude the header. The need for a header requires additional productiontime, as well as additional installation time.

Some heat exchanger designs have been found to be more efficient thanthe multiple-coil-on-tube head exchanger shown in FIG. 1. “Counter-flow”(or “contra-flow”) heat exchangers are known to be one of the mostefficient, or effective, classes of heat exchangers. In a counter-flowheat exchanger with a plurality of coils, the temperature differencebetween the liquids is substantially constant along its length.Generally, a cold water flow enters a coil at one end of the heatexchanger, and a warm water flow enters another coil at the other end ofthe heat exchanger. The warm water flow provided heat to the cold waterflow, and the warm water flow gets cooler as it travels along the heatexchanger, while the cold water flow gets warmer as it travels along theheat exchanger. If the cold and warm water flows were to enter the heatexchanger at the same end, there would be a large temperature differenceat the end, and a much smaller temperature difference at the other end.This parallel flow case is limited to a maximum heat exchangereffectiveness of about 50%.

Therefore, taking a look at the multiple-coil-on-tube heat exchanger ofFIG. 1. It is not a true “counter-flow” (or “contra-flow”) heatexchanger. The reason it is not a true counter-flow heat exchanger isthat the incoming cold stream is split so that part of it startshalf-way along, and part of it ends half-way along. To be a truecounter-flow heat exchanger, all of the first flow has to travel in asubstantially opposite direction to the second flow along the entirelength of the heat exchanger for both flows, in order to provide aconstant temperature difference along the length of the heat exchanger.For this, the input of the cold stream is generally at the opposite andof the heat exchanger from the input of the warm stream in acounter-flow heat exchanger.

In summary, although single-coil heat exchangers of the helicalcoil-on-tube type have reasonable production rates and perform wellsince they can be implemented as counter-flow heat exchangers, they canalso incur significant pressure losses. Multiple coil-on-tube heatexchangers are able to overcome some of the pressure loss problems ofsingle-coil designs, but they require additional headers to treat theliquids, and their performance is not as efficient as they could be,since they are not true counter-flow heat exchangers.

Therefore, it is desirable to have a type of heat exchanger thatprovides similar performance and production times to the single-coildesign, while improving on the lower efficiency and need for additionalequipment of the multiple-coil design.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate or mitigate at leastone disadvantage of previous coil-on-tube heat exchangers.

In a first aspect, the present invention provides a coil-on-tube heatexchanger having a center tube for a first liquid flow. The heatexchanger includes a plurality of coil tubes for a second liquid flow.The coil tubes are helically wrapped in a parallel relationship alongthe length of the center tube. Each of the plurality of coil tubes is incontact with the center tube and extending substantially along the samelength of the center tube.

Each of the plurality of coil tubes has an inlet end, and the inlet endsof each of the plurality of coil tubes are all preferably substantiallyco-located. Similarly, each of the plurality of coil tubes has an outletend, and the outlet ends of each of the plurality of coil tubes arepreferably substantilly co-located.

The first liquid flow and the second liquid flow are preferably inopposite directions, so as to provide a counter-flow heat exchanger. Theplurality of coil tubes is preferably arranged in a helix such thatthere is minimum space between each of the plurality of coil tubes. Theplurality of coil tubes preferably extend substantially along the entirelength of the center tube.

In a heat exchanger according to the present invention the plurality ofcoil tubes can form a first helix. The heat exchanger can furthercomprise a second plurality of coil tubes for a third liquid flow, thesecond plurality of coil tubes helically wrapped in a parallelrelationship along the length of the center tube to form a second helix,each of the second plurality of coil tubes being in contact with thecenter tube and extending substantially along the same length of thecenter tube, the second helix extending along a different length of thecenter tube than the first helix. The first helix and the second helixcan extend along substantially the entire length of the center tube.

The coil tubes can each have a substantially similar cross-sectionalprofile, such as a cross-sectional profile that is substantiallyrectangular or substantially annular, or a cross-sectional profile thathas a flat surface at an interface with the center tube. The pluralityof coil tubes can each have a substantially similar cross-sectionalarea, such that each coil tube is for receiving a substantially similarvolume of liquid flow. The plurality of coil tubes can be ofsubstantially equal size and/or length. The coil tubes can be wrappedaround the center tube in a clockwise direction, or a counter-clockwisedirection.

In a embodiment, the heat exchanger of the present invention furthercomprises an inlet header for splitting flow to the plurality of coiltubes at an inlet end of the helix. The inlet header can split incomingliquid flow into a plurality of parallel flows for travel along asubstantially similar path around the helix in the plurality of coiltubes. In an embodiment, the heat exchanger of the present inventionfurther comprises an outlet header for mixing flow from the plurality ofcoil tubes at an outlet end of the helix.

In another embodiment, the heat exchanger of further comprises aplurality of anchors for anchoring the plurality of coil tubes to thecenter tube, at the inlet end and/or the outlet end of each of the coiltubes.

The heat exchanger according to aspects of the present invention ispreferably used for wastewater heat recovery, where the first liquidflow is a drain water flow and the second liquid flow is a fresh waterflow, but many other applications exist.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the flowingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached Figures, wherein:

FIG. 1 illustrates a perspective view of a conventional coil-on-tubeheat exchanger;

FIG. 2 illustrates a perspective view of a coil-on-tube heat exchangeraccording to an embodiment of the present invention;

FIG. 3 illustrates a perspective view of a coil-on-tube heat exchangeraccording to another embodiment of the present invention;

FIG. 4 illustrates a perspective view of a coil-on-tube heat exchangeraccording to a further embodiment of the present invention including aplurality of helixes; and

FIG. 5 illustrates a perspective view of a coil-on-tube heat exchangeraccording to another embodiment of the present invention, including ainflow header and an outflow header; and

FIG. 6 illustrates a coil-on-tube heat exchanger according to a furtherembodiment of the present invention.

Generally, the present invention provides a coil on tube heat exchangerthat uses multiple parallel helical coil tubes to limit liquid pressurelosses while providing at least similar performance and production timesto previous coil and tube designs. Two or more coil tubes are wrappedtogether around a tube in a helical fashion, permitting the heatexchanger to be used in a “counter-flow” (or “contra-flow”)implementation. The system preferably includes a header (or manifold) toconnect two or more of the coils together at the beginning and/or end ofthe tube. However, each individual coil may be connected to a separateload and kept independent. Embodiments of the present invention providereduced pressure loss, higher performance and are generally faster tomanufacture than prior heat exchangers.

The term “counter-flow” (or “contra-flow”) is applied to a heatexchanger where the liquid flows are in opposing directions. This isdesirable as it results in the most efficient (or “effective”) classesof heat exchanger. In a counter-flow heat exchanger having a pluralityof coils, the temperature difference between the liquids issubstantially constant along the length of the heat exchanger. Ingeneral, to be a true counter-flow heat exchanger, all of a first liquidflow has to travel in a substantially opposite direction to a secondliquid flow. It should be noted that a heat exchanger may be designedand intended as a counter-flow heat exchanger but it not necessarily beinstalled in this manner if one side of the connections are installedreverse to what is intended.

The term “tube” or “coil tube” as used herein represent any stationarytube, pipe or channel, of any material that can be used to transportliquid. The present invention is not limited to pipes that arecylindrical in shape, as pipes of any cross-section may be used.

The term “flow-splitting” or other references to liquid flow being splitas used herein represents splitting flow, equally or not equally, fromone or more inflow tubes to a plurality of outflow tubes. The end resultis that the flow is split into multiple tubes so that a higher volume offlow can be treated with a modest pressure loss, as opposed to using asingle larger tube. For example, in a header or manifold, the incomingflow is split into two or more outgoing flows.

The term “liquid” as used herein represents any liquid, such as water, achemical substance, or any other aqueous solution, liquid or semi liquidsubstance, such as drain water, waste water or other waste liquid,sludge, grey water, black water or any liquid having solid and/orsemi-solid components.

The term “in a parallel relationship”, as used herein in relation tocoil tubes being helically wrapped in a parallel relationship along thelength of the center tube, represents the coil tubes being located sideby side and coiled together along the center tube. The parallelrelationship refers to the physical location of the tubes in relation toeach other.

The term “substantially co-located”, as used herein in relation to endsof coil tubes being substantially co-located, represents each of theends being located in substantially the same region of the center tubearound which they are wrapped. They can be at a particular end of thecenter tube, but can alternatively be at any point along the length ofthe center tube.

FIG. 2 illustrates a perspective view of a coil-on-tube heat exchangeraccording to an embodiment of the present invention. The heat exchanger100 includes a center tube 102 for a first liquid flow, such as drainwater flow, having a center tube inflow end 104 and a center tubeoutflow end 106. A plurality of coils, or coil tubes, 108 are providedfor a second liquid flow, such as fresh water flow, each having a coiltube inflow end 110 and a coil tube outflow end 112. The plurality ofcoil tubes 108 are helically wrapped in parallel with each other alongthe length of the center tube, preferably along substantially the entirelength of the center tube. In contrast to known counter-flow andcoil-on-tube heat exchangers, each of the plurality of coil tubes 108 isin contact with the center tube 102. Each of the plurality of coil tubes108 also extends substantially along the same length of the center tube,preferably along substantially the entire length of the center tube.

Embodiments of the present invention are preferably used to recover heatfrom warm flows of wastewater, but the invention is not limited to theseapplications. For example, the heat from wastewater in the center tube102 flowing in a direction F1 is preferably used to heat freshwaterflowing in a direction F2 in the plurality of coil tubes 108. For thisreason, it is advantageous according to embodiments of the presentinvention that each of the plurality of coil tubes 108 is in contactwith the center tube 102, so that the benefit of the warm flows ofwastewater can be applied to liquid flowing in each of the plurality ofcoil tubes 108. Although the liquid flows in the coil tubes 108 in adirection that appears somewhat perpendicular to F1, the liquid in thecoil tubes 108 progresses along the heat exchanger in a direction F2,and therefore creates a counter-flow heat-exchanger.

Though the embodiment of FIG. 2 is shown with the liquid flows F1 and F2so that the heat exchanger is a counter-flow heat exchanger, the samedevice can be used with liquid flows F1 and F2 being in substantiallysimilar, or substantially parallel, directions. Occasionally this is adesirable method of installation, as is known to those of skill in theart.

With the design of a heat exchanger 100 as shown in FIG. 2, theplurality of coil tubes can be two or more tubes that are wrappedtogether around the center tube to form a helix. A result of this designis that in a presently preferred embodiment, the flows of liquid throughthe plurality of coil tubes 108 begin/end at the same end of the tube102, forming a counter-flow heat exchanger. In other words, the coiltube inflow ends 110 are preferably each provided at or near the centertube inflow end 104. The coil tube outflow ends 112 are preferably eachprovided at or near the center tube outflow end 106. This provides alower loss in liquid pressure through the coil tubes 108 as opposed to aheat exchanger having a single helical around the center tube, as isknown in the prior art.

To summarize the general embodiment shown in FIG. 2, a coil-on-tube heatexchanger is provided having a center tube for a first liquid flow. Theheat exchanger includes a plurality of coil tubes for a second liquidflow. The coil tubes are helically wrapped in parallel with each otheralong the length of the center tube. Each of the plurality of coil tubesis in contact with the center tube and extends substantially along thesame length of the center tube, preferably substantially along theentire length of the center tube. The heat exchanger according toaspects of the present invention is commonly used for wastewater heatrecovery, where the first liquid flow is a drain water flow and thesecond liquid flow is a fresh water flow.

FIG. 3 illustrates a coil-on-tube heat exchanger according to anotherembodiment of the present invention. As mentioned earlier, embodimentsof the present invention provide that each of the plurality of coiltubes extends substantially along the same length of the center tube. Inthe embodiment of FIG. 2, the coil tubes 108 extend substantially alongthe entire length of the center tube 102. However, this is not alwaysdesired. In the embodiment of FIG. 3, the plurality of coils extendsubstantially along the same length of the center tube 102, but do notextend substantially along the entire length of the center tube. Thisembodiment illustrates that the helix formed by the plurality of coiltubes 108 can start part way along the center tube 102, and can end partway along the center tube 102.

In this particular embodiment, the helix of five coil tubes extendsalong about half the length of the center tube 102. The coil tube inflowends 110 of the coil tubes 108 are provided substantially at the centertube outflow end 106, and the coil tube outflow ends 112 are provided ata point along the length of the center tube 102, such as about half-wayalong in the case of FIG. 3.

An implementation such as in FIG. 3 is advantageous for certainapplications. For instance, in a situation where a heat exchangeraccording to an embodiment of the present invention is to be installedin a house having abrupt elbow joints, the heat exchanger of FIG. 3 maypreferably be used. Having a bare center tube 102 to mate with the elbowpermits a better and more even drain water coating of the inside wall ofthe center pipe if a leading edge is provided, as opposed to the helixextending along that portion. Moreover, the coil tubes 108 contributethe majority of the weight and material cost of a heat exchangeraccording to embodiments of the present invention. Therefore, insituations where having the helix extend only along a portion of thelength of the center tube is needed or preferred, this can result incost savings in terms of heat exchanger production.

The embodiments described in relation to FIG. 2 and FIG. 3 show a heatexchanger with a single helix formed by the plurality of coil tubes 108.Further embodiments of the present invention include a plurality of suchhelixes. FIG. 4 illustrates a heat exchanger according to a furtherembodiment of the present invention including a plurality of helixes. Afirst and second helix 114 and 116 include a first and second pluralityof coil tubes 118 and 120, respectively. As illustrated in FIG. 4, thehelixes can be of different lengths, and can include a different numberof coil tubes. For example, helix 114 extends along about ⅔ of thelength of the center tube 102 and includes four coil tubes 118, whilehelix 116 extends along about ⅓ of the length of the center tube 102 andincludes two coil tubes 120.

An implementation such as in FIG. 4 is advantageous for certainapplications, such as some industrial applications, in which a firstliquid flow and a second liquid flow may be advantageously kept atdifferent temperatures. For instance, a first liquid flow can be usedfor cleaning floors, and is desired to be kept at a high temperature. Asecond liquid flow can be used for another process, such as a chemicalprocess, in which the liquid temperature is to be kept within a certaintemperature range, for example below 30 degrees Celsius. In such a case,an embodiment of the present invention such as illustrated in FIG. 4 canadvantageously be employed, providing the advantages of the presentinvention, with some of the flexibility of feeding separate liquid flowsas in FIG. 1. Moreover, manufacturing of smaller helixes can be easier,and may be preferable when a high number of parallel coils is used. Asillustrated in FIG. 4, the helixes need not cover the entire length ofthe center tube 102. Such an implementation can be useful in situationswhere physical limitations exist in a location where the heat exchangeris to be installed, and it may not be necessary to have the coil tubescovering a particular portion of the center tube.

The coil tubes 108 are not limited to tubes of the same cross-section orof any specific cross-section. Any number of tubes of differingcross-sectional shapes/profiles and sizes may be coiled in parallel toform the heat exchanger. In a preferred embodiment, the coil tubes 108are of substantially equal, or substantially similar, cross-sectionalarea so as to treat a substantially similar volume of flow through eachtube. However, in alternative embodiments of the present invention, eachcoil tube 108 can be of differing cross-sectional size and profile. Theplurality of coil tubes can each have a substantially similarcross-sectional profile, such as a cross-sectional profile that issubstantially rectangular or substantially annular. The cross-sectionalprofile can alternatively have a flat surface at an interface with thecenter tube, and not necessarily have a flat surface on the parts thatdo not interface with the center tube. The cross-sectional profiles canbe dimensioned so that each coil tube is for receiving a substantiallysimilar volume of liquid flow. The plurality of coil tubes can be ofsubstantially equal size and/or length.

The plurality of coil tubes 108 can be referred to collectively as ahelix. The pitch of the helix can preferably be adjusted according tothe number of coil tubes being used, so that the distance between wrapsand coil tubes is minimized, though this space may be varied and neednot be constant. Thus the plurality of coil tubes can be wrapped aroundthe center tube most efficiently without leaving significant spacebetween succeeding wrappings of tube and thereby making maximum use ofthe heat transfer area available. In other words, the plurality of coiltubes is preferably arranged in a helix such that there is minimum spacebetween each of the plurality of coil tubes. As compared to prior artsingle coil-on-tube heat exchangers, and those that use multiple coilseach covering a different longitudinal area of the center tube,embodiments of the present invention have a pitch that is higher. Forexample, when each of the coil tubes is of the same width, in betweeneach ring or wind of a particular coil tube are provided the other(s) ofthe plurality of coil tubes.

A particular embodiment is provided in FIG. 5, which shows a perspectiveview of a counter-flow coil-on-tube heat exchanger according to anembodiment of the present invention, including a header or manifold. Theembodiment in FIG. 5 illustrates a counter-flow coil-on-tube heatexchanger with six parallel coil tubes 108. The flow of liquid is split,in this embodiment, at an inflow end of the helix, using an inflowheader 122, to the plurality of coil tubes 108. The inlet header canthus split incoming liquid flow into a plurality of parallel flows fortravel along a substantially similar path around the helix in theplurality of coil tubes. A similar outflow header 124 mixes the multipleflows in the plurality of coil tubes 108 back into a single flow at theoutflow end of the helix. As mentioned earlier, the inflow end of thehelix is preferably provided at or near the center tube outflow end 106,and the outflow end of the helix is preferably provided at or near thecenter tube inflow end 108. The incoming liquid flow is thus split intoa plurality of parallel flows that travel a substantially similar patharound the helix, in a direction opposing that of the flow through thecenter tube. Relative to prior designs having a single helical coil, theloss in pressure as the liquid travels through the coil tubes is muchlower.

FIG. 6 illustrates a coil-on-tube heat exchanger acording to a furtherembodiment of the present invention. A header or manifold is not shownin order to illustrate that each of the plurality of channels onlycompletes a single wrapping of the center tube.

It is worth noting that a header, or manifold, or a plurality thereofcan be provided with any of the embodiments of the present invention.For instance, a pair of inflow and outflow headers can be suitably usedwith the embodiment shown in FIG. 4.

Of course, a heat exchanger according to embodiments of the presentinvention does not need a header to operate. For example, the pluralityof coil tubes can have many different liquid inputs. As such, each ofthese different liquid inputs can benefit from the heat exchanger,without having to be processed together. The different liquid flows inthe plurality of coil tubes can each be processed separately at theinlet and outlet ends of the helix. Also, there can be any combinationof headers (zero to many) at the inlet and outlet.

For convenience, the presently preferred embodiment of the presentinvention uses standard available sizes and diameters of copper tube. Ofcourse, any other tube diameter, shape, or material may be used for thecenter tube or coil tubes. As larger contact areas between each of theplurality of coil tubes 108 and center tube 102 aid heat transfer, thepreferred embodiment of the invention includes helical coil tubes havinga substantially flattened, or rectangular, cross-sectional profile.Although this feature is preferred for reasons of performance, thecross-sectional profile of the coil tube is by no means limited to thisshape for the present invention.

In order to limit liquid pressure losses to a modest quantity fordifferent sizes of heat exchangers, the present embodiments of theinvention use different numbers of coil tubes. Although presentlypreferred embodiments use 2 to 6 coil tubes, the invention is notlimited to this range. For example, an embodiment of the invention canhave a multiplicity of coil tubes that is the maximum number that can bewound around the center tube, so that essentially the heat exchanger hasa series of “rings” up the tube, since each coil tube would onlycomplete a single wrapping of the center tube.

Due to the production process, the presently preferred embodiment of theinvention uses coil tubes that are wrapped around the center tube in acounter-clockwise direction. Wrapping the coil tubes in a clockwisedirection would still fall into the scope of the present invention. Thecoil tubes are preferably anchored to the center tube at each end by ananchor. The anchors can be provided at the inlet end and/or the outletend of each of the coil tubes. The anchor can be provided by anysuitable means, such as brazing or welding, in order to maintain thetension in the tubes that will keep them wrapped tightly around the pipeand thereby ensure good thermal contact.

In summary, a coil on tube heat exchanger is provided that uses multipleparallel helical coil tubes to limit liquid pressure losses whileproviding at least similar performance and production times to previouscoil and tube designs. A plurality of coil tubes are helically wrappedtogether around a center tube in parallel with each other, therebyforming a counter-flow heat exchanger. The system can include a header,or manifold, to connect two or more of the coils together at thebeginning and/or end of the tube. However, each individual coil canalternatively be connected to a separate load and kept independent, andtherefore a header is not required for the functioning of the invention.Embodiments of the present invention advantageously provide reducedpressure loss, higher performance and are generally faster and easier tomanufacture than prior heat exchangers.

The above-described embodiments of the present invention are intended tobe examples only. Alterations, modifications and variations may beeffected to the particular embodiments by those of skill in the artwithout departing from the scope of the invention, which is definedsolely by the claims appended hereto.

1. A coil-on-tube heat exchanger having a center tube for a first liquidflow, the heat exchanger comprising: a plurality of channels for asecond liquid flow, the plurality of channels helically wrapped in aparallel relationship along the length of the center tube, each of theplurality of channels being in contact with the center tube andextending substantially along the same length of the center tube suchthat each of the plurality of channels only completes a single wrappingof the center tube, and each of the plurality of channels is arrangedsuch that there is minimum spacing between each of the plurality ofchannels.
 2. The heat exchanger of claim 1 wherein the first liquid flowand the second liquid flow are in opposite directions, so as to providea counter-flow heat exchanger.
 3. The heat exchanger of claim 1 whereineach of the plurality of channels has an inlet end, the inlet ends ofeach of the plurality of channels being co-located.
 4. The heatexchanger of claim 1 wherein each of the plurality of channels has anoutlet end, the outlet ends of each of the plurality of channels beingco-located.
 5. The heat exchanger of claim 1 wherein the plurality ofchannels extend substantially along the entire length of the centertube.
 6. The heat exchanger of claim 1 wherein the plurality of channelsforms a first helix, the heat exchanger further comprising a secondplurality of channels for a third liquid flow, the second plurality ofchannels helically wrapped in a parallel relationship along the lengthof the center tube to form a second helix, each of the second pluralityof channels being in contact with the center tube and extendingsubstantially along the same length of the center tube, the second helixextending along a different length of the center tube than the firsthelix.
 7. The heat exchanger of claim 6 wherein the first helix and thesecond helix extend along substantially the entire length of the centertube.
 8. The heat exchanger of claim 1 wherein each of the plurality ofchannels has a substantially similar cross-sectional profile.
 9. Theheat exchanger of claim 1 wherein each of the plurality of channels hasa substantially rectangular cross-sectional profile.
 10. The heatexchanger of claim 1 wherein each of the plurality of channels has asubstantially similar cross-sectional area.
 11. The heat exchanger ofclaim 1 further comprising an inlet header for splitting flow to theplurality of channels at an inlet end of the helix.
 12. The heatexchanges of claim 11 wherein the header splits incoming liquid flowinto a plurality of parallel flows for travel along a substantiallysimilar path around the helix in the plurality of channels.
 13. The heatexchanger of claim 1 further comprising an outlet header for mixing flowfrom the plurality of channels at an outlet end of the helix.
 14. Theheat exchanger of claim 1 further comprising a plurality of anchors foranchoring the plurality of channels to the center tube.
 15. The heatexchanger of claim 1 wherein at least some of the plurality of channelsare provided as a plurality of coil tubes.
 16. The heat exchanger ofclaim 1 wherein the plurality of channels are provided as a plurality ofcoil tubes.
 17. Use of the heat exchanger of claim 1 for the exchange ofheat from the first liquid flow to the second liquid flow, comprisingthe steps of flowing a first liquid through the center tube and flowinga second liquid through the plurality of channels wherein the firstliquid flow is a waste water flow.